(132d) Citrus Waste Biorefinery: Pretreatment and Enzymatic Hydrolysis Processes

Conversion of agro-industrial wastes to biofuels is an emerging technology, and important strategy to reduce dependence on foreign fuels. Citrus waste (Peel, pulp, and seeds) generated from juice production are almost 50 w% of the original whole fruit. The US 2006/08 seasons citrus juice production generated approximately 10.6 millions of metric tons of waste, which is currently processed as a low-value cattle feedstock. At times, the high-costs of waste drying and processing production and poor markets can result in environmental disposal problems. Citrus waste is a low-lignin, and pectin-rich biomass that can be converted to ethanol and other high-valued products, consisting of soluble sugars, water, and insoluble polysaccharides (cellulose, hemicelluloses, pectin, and lignin-like compounds) which must be pretreated, and hydrolyzed before a biorefinery process. The objective of this project is to develop the basis for a technically and economically feasible biorefinery process for approximately 40,000 to 60,000 tons/year of citrus waste generated during the production of Rio Red Grapefruit juice in a facility located in Mission, TX. The research is focused on the enhancement of pretreatment and hydrolysis to convert the polysaccharides into fermentable monosaccharides (mainly into glucose, fructose, galacturonic acid, and pentoses). The pretreatment will provide the optimal particle surface area required in the subsequent enzymatic hydrolysis of insoluble polysaccharides. Citrus waste have been reduced to micrometric size and hydrolyzed using different commercial preparations of enzymes containing cellulases, pectinases, b-glucosidase and xylanases to obtain soluble monosaccharides to be used as platform for biorefinery processes. Engineering concepts such as reaction rate, enzymes loadings, and sugars yields, and scale up factors will be modeled from the information generated during bench-top and mini-pilot experiments. The preliminary results demonstrated that Rio Red grapefruit processing waste have a considerable concentration of soluble sugars and structural polysaccharides. Furthermore, first experiments on enzymatic hydrolysis of waste with different particle size shown that at lower initial particle sizes, higher enzymatic reaction rates and conversions of cellulose, hemicellulose, and pectin to reducing sugars were observed.